The invention relates to an infinitely variable power transmission mechanism for use in transmitting torque from a torque input element to a torque output element with a wide torque ratio range.
Infinitely variable torque ratio characteristics for a power transmission can be achieved by using a friction belt and pulley arrangement in which a drive pulley and a driven pulley, connected by an endless belt, are adapted for torque transfer with an infinitely variable torque ratio range by adjusting the pitch diameter of the pulleys, the pitch diameter of the driving pulley increasing as the pitch diameter of the driven pulley decreases, and vice versa. Examples of belt drives of this kind may be seen by referring to U.S. Pat. Nos. 5,417,621 and 5,514,047.
It is known design practice also to provide infinitely variable torque ratio characteristics by using a hydraulic pump as a driving member and a hydraulic motor as a driven member. The pump and motor are located in a closed hydrostatic fluid pressure circuit. By varying the displacement of the pump, the effective speed ratio of the hydrostatic transmission can be changed through a wide torque ratio range.
Various types of infinitely variable friction drives also are well known. It is known design practice, for example, to use friction cone members wherein the relative positions of the friction cones are adjustable to provide an infinitely variable torque ratio characteristic. An example of a friction cone drive mechanism may be seen by referring to U.S. Pat. No. 5,681,235.
If an infinitely variable transmission is used with an internal combustion engine to deliver torque to driven members, such as vehicle traction wheels, the infinitely variable transmission characteristics can be matched with the engine speed/torque characteristics such that the engine may be operated with an engine throttle setting that will correspond to a speed consistent with minimum brake specific fuel consumption as variable torques are commanded by the operator. In this way, the continuously variable transmission improves the overall driveline efficiency.
The invention is a torque transfer method and an infinitely variable drive that comprises a rotary, generally conical driving member and a rotary, generally conical driven member. The driving and driven members are mounted for rotation, respectively, on a torque input shaft axis and a torque output shaft axis. Each carries needles on its surface. The needles mesh, thereby permitting torque transfer between the driving and driven members.
Although the invention may be used in a driveline with an internal combustion engine, it may be used also in other design applications: e.g., accessory drives, window regulators, machine tool drives, etc.
The infinitely variable drive of the invention transmits torque from a rotary torque input shaft to a rotary torque output shaft through the rotary driving and driven members. The shafts have axes that are spaced, one with respect to the other. Each member has a generally conical surface, each surface having a continuously curved profile that extends from one axial end thereof to the other. The driving and driven members rotate on their respective shaft axes. Each member has a cluster of torque transmitting needles on its surface. The needles of the driving member mesh with the needles of the driven area in an area of mesh as torque is transmitted between the members.
The surfaces of the rotary members of the invention are curved, rather than precisely of conical shape, and are defined as surfaces of revolution. The surfaces are in engagement, one with respect to the other, so that torque is transmitted between the rotary members. The angle of the axis of revolution of one member relative to the axis of revolution of the other member can be changed so that the position of the area of mesh of the needles on the surface of one member and the needles of the other member will change.
The rotary members will be referred to, for purposes of this description, as cone members. It should be understood, however, that their surfaces of revolution are not precisely conical. Further, the profile of each rotary member is curved, but the rotary members are not necessarily hemispherical. Incremental areas of the surfaces of revolution at various locations along the axis of rotation may have differing radii of curvature.
Unlike conventional conical drive mechanisms of the kind shown, for example, in the previously mentioned ""235 patent, the area of mesh between the driving and driven members of the invention is not characterized by incremental portions of the area of contact of the driving and driven members that have differential speeds. This is due to the fact that the area of mesh is not characterized by frictional contact between the surfaces of the driving and driven members. The area of mesh is characterized instead by intermeshing needle elements densely formed on the surfaces of each of the rotating members. The needles themselves are in frictional engagement at the area of mesh as torque is distributed from one cone member to the other. Differential movement of incremental portions of the area of mesh for the respective rotating members is accommodated by flexure of the intermeshing needles. This flexure of the needles will permit continuous, efficient torque transfer between the members throughout the entire ratio range of the transmission. The flexure is coincident with frictional sliding motion of the needles of one cone member relative to the needles of the other cone.
Known friction cone drives typically have frictional contact between the surfaces of friction cones. In actual practice, the cones do not engage at a single point. Rather, a so-called contact patch is established between the cones. Friction torque at the contact patch is developed by a tangential force component on the surface of each cone member. Because of the geometry of the conical surfaces, the contact patch has incremental areas where sliding motion will occur between the conical surfaces of the driving and driven members within the contact patch. This sliding motion requires the presence of a hydraulic lubricating oil film to avoid galling and deterioration of the friction surfaces of the conical members. The presence of an oil film, however, is imperfect protection against deterioration and wear of the friction surfaces, especially when the transmission is operated in a high torque range. The torque transfer between the driving and driven members of the present invention, unlike torque transfer in such conventional friction cone drives, takes place without the presence of a contact patch between the members. The flexure of the intermeshed needles of applicant""s invention accommodate differential tangential velocities of the incremental portions of the contact areas of the members when the needles are in meshing engagement.
U.S. Pat. No. 4,028,949 discloses a linear transmission wherein motion of a driving strip can be transmitted to a driven strip with a ratio of unity. The motion transfer occurs through an endless belt carrying bristles that mesh with bristles on the linearly movable strips. It is not possible in an arrangement of this type to provide for infinitely variable ratio characteristics.
The transmission of the invention makes provision for adjusting the angularity of the rotating axis of each member in a continuous and smooth fashion without the requirement for high adjustment forces. The angularity of the conical members can be changed during torque transfer so that the overall torque ratio can be varied without interrupting the operation of the transmission.
The invention is capable of developing a wide range of ratios with elements that are assembled with an economy of space. In one embodiment of the invention, a ratio range of 10:1 to 0.4:1 has been successfully demonstrated. A torque capacity of 200 lb. -ft. or more easily can be accommodated using elements with a gross weight of 50 lbs. or less. It is emphasized, however, that these features are representative of only one embodiment of the invention. The torque capacity, for example, may be greater or less, depending on the design requirements.